The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the body adjacent to nerves or other sensitive body structures, such as the head and neck, the spine, the brain and the like.
Many surgical procedures involve the treatment and/or removal of soft tissue closely adjacent to other non-target body structures, such as nerves, bone or cartilage (e.g., articular cartilage). One of the major difficulties with these procedures is discriminating between the target soft tissue and the non-target body structure, and then being capable of removing or otherwise modifying the soft tissue without damaging the non-target structure. Particularly troublesome are those surgical procedures which require the surgeon to remove tissue adjacent to nerves (the cordlike structures which convey impulses between a part of the central nervous system and a region of the body).
Many surgical procedures require the manipulation of surgical instruments in and around important nerves in the body. For example, surgical procedures within the nasal cavity (e.g., FESS procedures) often require the surgeon to remove polyps, turbinates or other sinus tissue adjacent to the optic or olfactory nerves, which are the central processes for sight and smell. Surgical procedures within the mouth often involves ablation or contraction of tissue (e.g., in the tongue or uvula) near the hypoglossal nerve, which controls movements of the tongue. Similarly, in spinal procedures (e.g., treatment of herniated discs or spinal fusion), the surgeon must often remove or modify tissue closely adjacent to the spinal nerves near their roots at the spinal cord. One of the significant problems with these procedures is that conventional surgical instruments generally do not differentiate between the target tissue and the surrounding nerves, which may result in nerve injury of impairment of nerve function. Nerve injury can lead to muscle paralysis, pain, exaggerated reflexes, loss of bladder control, impaired cough reflexes, spasticity and other conditions. Moreover, the neurons within some nerves typically do not regenerate after injury.
In the past several years, powered instrumentation, such as microdebrider devices and lasers, has been used to treat tissue in various procedures, such as removing polyps or other swollen tissue in functional endoscopic sinus surgery. Microdebriders are disposable motorized cutters having a rotating shaft with a serrated distal tip for cutting and resecting tissue. The handle of the microdebrider is typically hollow, and it accommodates a small vacuum, which serves to aspirate debris. In this procedure, the distal tip of the shaft is delivered to the target site, and an external motor rotates the shaft and the serrated tip, allowing the tip to cut tissue at the target site, such as sinus tissue, spinal tissue, or the like. While microdebriders have been promising, they are not very precise, and it is often difficult, during the procedure, to differentiate between the target tissue, and other neighboring body structures, such as cartilage, bone or nerves. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone at the target site, and to avoid damaging the nerves that extend through the target site.
Lasers were initially considered ideal for many surgical procedures because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, cartilage, bone and/or nerves often lie within close proximity of the target tissue, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Recently, RF energy has been used to remove or otherwise treat tissue in open and endoscopic procedures. This procedure typically involves the use of a monopolar electrode that directs RF current into the target tissue to desiccate or destroy tissue in the tongue. Of course, such monopolar devices suffer from the disadvantage that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large distance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures in regions of the patient""s body adjacent to non-target body structures, such as nerves, cartilage and bone. The systems and methods of the present invention are particularly useful for ablation, resection, contraction and hemostatis of soft tissue that is closely adjacent to nerves, such as tissue within the head and neck, the spine, the brain and the like.
Methods of the present invention comprise positioning an electrosurgical instrument, such as a probe or catheter, in close proximity to a first body structure adjacent to a second body structure so that one or more electrode terminal(s) are brought into at least partial contact or close proximity with the first and second body structures. High frequency voltage is then applied between the electrode terminal(s) and one or more return electrode(s) to cut, remove, ablate, contract, coagulate, vaporize, desiccate or otherwise modify the first body structure without damaging the second body structure. The first body structure is typically soft tissue, such as sinus, mucosal, spinal, or brain tissue, and the second body structure typically comprises a structure either having different electrical or molecular properties than soft tissue, such as bone, cartilage, adipose tissue, nerves and the like. The present invention provides a method for automatically discriminating between the two body structures such that the soft tissue is removed or otherwise modified, while the second structure is left relatively unaffected by the procedure.
In one aspect of the invention, a method is provided for removing or ablating soft tissue that is adjacent to a nerve structure, such as swollen nasal tissue within the sinuses, disc tissue within the spine, tumor tissue within the brain and the like. In this method, one or more electrode terminal(s) are positioned adjacent to the target tissue, either endoscopically, transluminally, or directly in an open procedure. An electrically conductive fluid, such as isotonic saline, is delivered to the target site to substantially surround the electrode terminal(s) with the fluid. Alternatively, a more viscous fluid, such as an electrically conductive gel, may be applied to the target site such that the electrode terminal(s) are submerged within the gel during the procedure. In both embodiments, high frequency voltage is applied between the electrode terminal(s) and one or more return electrode(s) to remove at least a portion of the tissue. According to the present invention, the electrical energy is selectively applied to soft tissue to ablate this tissue, while minimizing energy delivery to the adjacent nerves. In particular, applicant has found that the present invention is capable of completely removing soft tissue closely adjacent to nerves without causing nerve function impairment or any significant changes to the tissue in nerve fibers or the surrounding epineurium.
In one embodiment, the soft tissue is removed by molecular dissociation or disintegration processes. In this embodiment, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the electrode terminal(s) and the soft tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. The small depths of collateral tissue damage provided by the present invention allows the surgeon to remove tissue close to a nerve without causing collateral damage to the nerve fibers. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference
In another embodiment, systems and methods are provided for distinguishing between the fatty tissue (e.g., adipose tissue) immediately surrounding nerve fibers and the normal tissue that is to be removed during the procedure. Nerves usually comprise a connective tissue sheath, or epineurium, enclosing the bundles of nerve fibers to protect these nerve fibers. This protective tissue sheath comprises a fatty tissue (e.g., adipose tissue) having substantially different electrical properties than the normal target tissue. The system of the present invention measures the electrical properties of the tissue at the tip of the probe with one or more electrode terminal(s). These electrical properties may include electrical conductivity at one, several or a range of frequencies (e.g., in the range from 1 kHz to 100 MHz), dielectric constant, capacitance or combinations of these. In this embodiment, an audible signal may be produced when the sensing electrode(s) at the tip of the probe detects the fatty tissue surrounding a nerve, or direct feedback control can be provided to only supply power to the electrode terminal(s) either individually or to the complete array of electrodes, if and when the tissue encountered at the tip or working end of the probe is normal tissue based on the measured electrical properties.
In yet another embodiment, applicant has discovered that the mechanisms of the present invention can be manipulated to ablate or remove certain tissue structures, while having little effect on other body structures. As discussed above, the present invention employs a technique of vaporizing electrically conductive fluid to form a plasma layer or pocket around the electrode terminal(s), and then inducing the discharge of energy from this plasma or vapor layer to break the molecular bonds of the tissue structure. Energy evolved by the energetic electrons (e.g., 4 to 5 eV) can subsequently bombard a molecule and break its bonds, dissociating a molecule into free radicals, which then combine into final gaseous or liquid species. The energy evolved by the energetic electrons may be varied by adjusting a variety of factors, such as: the number of electrode terminals; electrode size and spacing; electrode surface area; asperities and sharp edges on the electrode surfaces; electrode materials; applied voltage and power; current limiting means, such as inductors; electrical conductivity of the fluid in contact with the electrodes; density of the fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons. Since different tissue structures have different molecular bonds, the present invention can be configured to break the molecular bonds of certain tissue, while having too low an energy to break the molecular bonds of other tissue. For example, fatty tissue, (e.g., adipose) tissue has double bonds that require a substantially higher energy level than 4 to 5 eV to break. In an exemplary embodiment, the present invention does not ablate or remove such fatty tissue.
In another aspect of the invention, a method includes positioning one or more electrode terminal(s) in close proximity to a target site adjacent to a nerve structure. High frequency voltage is applied to the electrode terminal(s) to elevate the temperature of collagen fibers within the tissue at the target site from body temperature (about 37xc2x0 C.) to a tissue temperature in the range of about 45xc2x0 C. to 90xc2x0 C., usually about 60xc2x0 C. to 70xc2x0 C., to substantially irreversibly contract these collagen fibers without damaging the nerve. In a preferred embodiment, an electrically conducting fluid is provided between the electrode terminal(s) and one or more return electrode(s) positioned proximal to the electrode terminal(s) to provide a current flow path from the electrode terminal(s) away from the tissue to the return electrode(s).
The current flow path may be generated by directing an electrically conducting fluid along a fluid path past the return electrode and to the target site, or by locating a viscous electrically conducting fluid, such as a gel, at the target site, and submersing the electrode terminal(s) and the return electrode(s) within the conductive gel. The collagen fibers may be heated either by passing the electric current through the tissue to a selected depth before the current returns to the return electrode(s) and/or by heating the electrically conducting fluid and generating a jet or plume of heated fluid, which is directed towards the target tissue. In the latter embodiment, the electric current may not pass into the tissue at all. In both embodiments, the heated fluid and/or the electric current elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers.
The contraction of collagen tissue is particularly useful in procedures for treating obstructive sleep disorders, such as snoring or sleep apnea, and for treating herniated discs by shrinking the nucleus pulposis of the herniated disc. In the former procedure, one or more electrode terminal(s) are introduced into the patient""s mouth, and positioned adjacent the target tissue, selected portions of the tongue, tonsils, soft palate tissues (e.g., the uvula), hard tissue and mucosal tissue. An endoscope or other type of viewing device, may also be introduced, or partially introduced, into the mouth to allow the surgeon to view the procedure (the viewing device may be integral with, or separate from, the electrosurgical probe). Electrically conductive fluid is applied as described above, and high frequency voltage is applied to the electrode terminal(s) and one or more return electrode(s) to, for example, ablate or shrink sections of the uvula without causing unwanted nerve damage to nerves extending under and around the selected sections of tissue.